Without limiting the scope of the present invention, the background of the invention is described with reference to propylene polymerization and copolymerization reactors and systems. Conventional propylene polymerization systems have been operated with temperature and pressure ranges well below the critical region of propylene, for example, below a critical temperature (T.sub.c) of 197.2.degree. F. and a critical pressure of 655.4 psig. For example, in more than one conventional process the polymerization system is typically operated at a temperature of about 140.degree. F. and 180.degree. F. and a pressure in the range of 440 to 480 psig. Surprisingly, however, it has been discovered that with presently available propylene polymerization catalysts, production is increased if the systems are operated outside of the conventional temperature and pressure ranges previously employed.
However, in order to take advantage of the unexpected benefits of operating outside of conventional temperature and pressure ranges, it has been found necessary to provide a propylene pressurization vessel that is operated above the critical temperature and pressure range of propylene, e.g., in the supercritical state. Thus, there exists a need for a propylene polymerization system that includes a pressurization vessel adapted to operate outside of conventional parameters.